This invention generally relates to the art of measuring compressive forces within a tablet-making machine. In particular, this invention relates to a method of checking a pickup load cell provided in a tablet-making machine for measuring and adjusting compressive forces applied to tablets being formed.
In a typical prior-art rotary tableting machine, powder material to be tableted is introduced successively into a plurality of tablet-forming dies that are supported by a rotary table. The powder thus introduced is held between upper and lower punches within the dies, and as the rotary table moves the punches through pressure rollers, the powder in each of the dies is compressed by the punches into a tablet. In this type of tableting machine, a compressive force applied to a tablet during the tablet-forming process is detected by an electric strain meter comprising a pickup load cell, and the data thus obtained are used to precisely control the amount of powder to be introduced into each tablet-forming die.
In order to check if the pickup load cell of the type described indicates exactly and precisely the compressive force on a tablet being formed, it has been customary to remove the pickup load cell from the tablet-making machine, and a change in the compressive force is examined by applying a pressure to the cell directly by a hydraulic machine.
However, this conventional method has inherent drawbacks such as that the mechanical means for transmitting the compressive force to the pickup load cell tends to suffer from loss of lubricating oil, resulting in reduction of transmission of the compressive force, and that some of the compressive force to be transmitted is lost by elongation of the mechanical component parts of the transmitting means due to mechanical fatigue, which leads to various mechanical errors. Therefore, if the pickup load cell is put back onto the tablet-making machine after the checking procedure, there often is a difference between the actual compressive force and the detected value thereof.
The above-described checking method has a further disadvantage that, when tablets of the same type are formed by a plurality of tablet-making machines, effective control of the compressive force applied to the tablets being formed cannot be administered in equal condition in all the machines if such forces change from machine to machine.